It is well-known that heat can cause a gas to expand and that heat-expanded gas can be used to move a volume of liquid. These phenomena are illustrated by the device of FIG. 1 comprising a pair of closed chambers 101 and 110 coupled by a conduit 106. Chamber 101 includes a liquid 104 extending above the opening of pipe 106 and a thermal radiation absorbing element 102, such as a black metal panel. When thermal radiation such as infrared radiation from the sun 100 strikes panel 102, the panel absorbs radiation and heats the gas in the chamber. The gas expands forcing liquid 104 up pipe 106 into upper chamber 110.
The potential effects of these phenomena can be estimated from the Ideal Gas Law which states: EQU PV=nkT (Eq. 1)
where P is the pressure, V is the volume, n is the number of molecules in the volume, k is Boltzman's constant, and T is the temperature relative to absolute zero. A quick experiment to estimate the available temperature rise from the sun is to place an aluminum sheet in a sealed clear plastic box. One side of the sheet is shiny aluminum, and the other side is painted flat black. The box is placed in the sun, first exposing the Al side to the light, and then the black side. Naturally, the black side absorbs more sunlight. A temperature difference of 20 to 30.degree. C. in full sun can be measured via a thermocouple inserted through a small hole into the chamber. In a well insulated chamber, higher temperatures are possible, but the insulation also slows losses during cooling.
A 30.degree. C. rise (remembering room temperature is about 300.degree. C. above absolute zero) causes a 10% change in pressure. This 10% pressure change can lift a column of water 10% of 33 feet (33 feet of water is the equivalent of one atmosphere of pressure), or 3.3 feet. On the other hand, the temperature rise can create a 10% volume change. So a 10.times.10.times.10 inch heated container can create a volume change of 100 cu in, or roughly 4.times.4.times.4 inches.
To see how this heat energy can be used to move a volume of liquid, consider the effect in FIG. 1. Here, sun 100 strikes the black metal sheet 102 in chamber 101. This sheet heats the air in chamber 101, raising the air's temperature by .about.10%. The increased air pressure pushes on liquid 104, which is forced through pipe 106 up into the second chamber 110. As long as the height of chamber 110 is less than 3.3 feet above chamber 101, liquid 104 can rise into chamber 110. The liquid will continue to rise until it has increased the volume of chamber 101 containing air by no more than about 10%.
While the device of FIG. 1 illustrates the relevant phenomena, it is a relatively stationary device with limited capacity to amuse or arouse curiosity. Accordingly there is a need for a more dynamic device to exhibit the effects of gas expansion and liquid displacement.